Projection exposure systems having a reflective reticle have been used in the past, inter alia, together with 1:1 Dyson objectives. These projection exposure systems are described in the following publications:    a) Owen et al, “⅛ μm optical lithography” J. Vac. Sci. B 10 (1992), pages 3032 to 3036, especially Parts B and C;    b) Pease et al, “Lithography for 0.25 μm and below . . . ” IEEE Symp. VLSI Technology (1992), pages 116 and 117;    c) Jeong et al, “Optical projection system . . . ” J. Vac. Sci. B 11 (1993), pages 2675 to 2679; and,    d) U.S. Pat. No. 4,964,705.
The incoupling of the illumination takes place via a partially transmitting mirror as shown, for example, in U.S. Pat. No. 4,964,705 (FIGS. 3A and 3B). Beam splitter cubes or beam splitter plates are not provided in these designs.
Reflective reticles are used exclusively in the area of lithography utilizing soft X-rays (EUVL). The beam splitting of illuminating and imaging beam paths is realized by an inclined incidence of the illumination. Beam splitter cubes or beam splitter plates are not used. The objectives are pure mirror objectives having a non-axial symmetrical beam path. The inclined incidence of the illuminating light on the reflective reticle has the disadvantage that the raised mask struts lead to vignetting.
Japanese patent publication 9-017719 discloses a wafer projection exposure system having a reflex LCD as a special reticle. According to FIG. 1 of this publication, a planar beam splitter plate is used to separate the illuminating and imaging beam paths. Illuminating system and projection objective are operated with a field symmetrical to the optical axis. The incoupling of the illuminating light via a beam splitter plate directly ahead of the reticle as shown in Japanese patent publication 9-017719 requires, on the one hand, the corresponding entry intersection distance, and, on the other hand, the passthrough through the planar plate leads to the astigmatic deformation of the illuminating light between which disturbs the required clean pupil imaging.
U.S. Pat. No. 5,956,174 discloses a catadioptric microscope objective wherein the illuminating light is coupled in via a beam splitter cube between the microscope objective and the tube lens. This type of illumination is conventional in reflected light microscopes. The illuminating field sizes are only in the order of magnitude of 0.5 mm.
Catadioptric systems for wavelengths of 193 nm and 157 nm are known. Catadioptric projection objectives having beam splitter cubes without an intermediate image are shown, for example, in U.S. Pat. Nos. 5,742,436 and 5,880,891 incorporated herein by reference.
Catadioptric projection objectives having a beam splitter cube and an intermediate image are disclosed in U.S. Pat. No. 06/424,471  6,424,471.
Illuminating devices for microlithography are disclosed in U.S. Pat. No. 5,675,401 and U.S. Pat. No. 6,285,443. So-called REMA objectives for imaging a reticle masking device (REMA) into the plane of the reticle are disclosed in U.S. Pat. No. 5,982,558 and U.S. Pat. No. 6,366,410, also incorporated herein by reference. With these objectives, inter alia, the entry pupil of the downstream projection objective is illuminated.
The production of transmission reticles (that is, masks operated in transmission for microlithography) is difficult for deep ultraviolet wavelengths, especially 157 nm, inter alia, because of suitable transmitting carrier materials. The materials CaF2 or MgF2 can be considered. However, reticles made of CaF2 or MgF2 are difficult to process and are therefore very expensive. Furthermore, a reduction of the minimal structural size which can be applied to a semiconductor chip results because of absorption and the thermal expansion of the reticle resulting therefrom when there are multiple illuminations. When possible, materials such as MgF2 are avoided because they are also double refracting.
The alternative are reflective reticles. To reduce the requirements imposed on the reticle, it is advantageous when the projection objective is configured as a reduction objective and the reticle is imaged so as to be demagnified. The reticle can then be provided with larger structures.
In conventional reduction objectives, the use of reflective reticles is not easily possible. The typical entry intersection distance of, for example, 30 mm reduces the illumination at suitable angles of incidence.